Self-diffusivities as a function of temperature were computed for 29
different ionic liquids (ILs) covering a wide variety of cation and
anion classes. Ideal ionic conductivities (sigma(NE)) were estimated
from the self-diffusivities via the Nernst-Einstein relation. The ion
pair (IP) lifetimes (tau(IP)) and ion cage (IC) lifetimes (tau(IC)) of
each IL were also computed. A linear relationship between the calculated
self-diffusivities and the inverse of IP or IC lifetimes was observed. A
similar inverse linear relationship was also observed for ideal ionic
conductivity. These relationships were found to be independent of
temperature and the nature of the IL. These observations connect
macroscopic dynamic properties with local atomic-level motions and
strongly suggest that the dynamics of ILs are governed by a universal IP
or IC forming and breaking mechanism. Thus, in order to design an ionic
liquid with enhanced dynamics, one should consider how to minimize IP or
IC lifetimes.